What do cats, starlings and cane toads have in common? ... They’re all on the list of the 100 worst invasive species due to their ability to devastate native ecologies. But as well as environmental destruction, invasive species also represent a health risk, carrying diseases beyond their traditional ranges. The apple snail is one such culprit, implicated in the spread of rat lungworm, which causes a kind of meningitis in humans. Most predators avoid the molluscs' eggs which are protected by a chemical that attacks the digestive system. Pictured is the inside surface of the small intestine of a rat that’s eaten this chemical – it’s become covered in mucus and unable to properly absorb nutrients. Without animals to feed on the eggs, the snail population is exploding. Until predators evolve to neutralise the eggs’ defence, apple snails are likely to enjoy their notoriety for a long time to come.
Written by Jan Piotrowski
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